JP5847803B2 - Method for manufacturing piezoelectric substrate - Google Patents

Description

  This application claims priority based on Japanese Patent Application No. 2011-076265 filed on Mar. 30, 2011. The entire contents of that application are incorporated herein by reference.

  The technology disclosed in this specification relates to a method of manufacturing a piezoelectric substrate.

Various manufacturing methods have been proposed as a method for manufacturing a piezoelectric substrate. For example, Japanese Patent Application Publication No. 2007-084357 discloses a technique for firing a piezoelectric substrate using a setter made of ZrO ₂ to which Ca is added.

  The need for a thin piezoelectric substrate has been increasing, and in recent years, a piezoelectric substrate having a thickness of 30 μm or less has been demanded. However, a method for manufacturing a piezoelectric substrate having a thickness of 30 μm or less has not been established yet. Therefore, the present specification provides a manufacturing method capable of suitably manufacturing a piezoelectric substrate having a thickness of 30 μm or less.

The inventors of the present application have found that the following two problems arise when a piezoelectric substrate having a thickness of 30 μm or less is baked on a setter. One is that the piezoelectric substrate adheres to the setter. When the sticking occurs, the piezoelectric substrate is broken when the piezoelectric substrate is moved from the setter. The other is that the diffusion of atoms from the piezoelectric substrate to the setter occurs at the contact surface between the piezoelectric substrate and the setter, resulting in non-uniform characteristics of the piezoelectric body (the characteristics differ between the front and back surfaces of the piezoelectric substrate). It is). Both phenomena are problematic because they greatly affect the characteristics of the piezoelectric body. Even when these two problems do not occur when a piezoelectric substrate thicker than 30 μm is fired, these two problems arise when a piezoelectric substrate of 30 μm or less is fired under the same conditions. For example, FIGS. 6 to 8 show that by firing a green sheet having a composition of Pb _{1-y / 2 + x} (N _1-y Nb _y ) O _{3 + x} (where N is Ti _0.48 Zr _0.52 ), The piezoelectric substrate is manufactured with various thicknesses, and the sticking rate and the c / a front / back difference (a high c / a front / back difference means that atoms are diffused from the piezoelectric substrate to the setter). The evaluation results are shown. Graphs 8 to 8 in FIG. 6 to 8 represent the adhesion rate, and graph B represents the c / a front / back difference. FIG. 6 shows the evaluation results when x = 0.0045 and y = 0.020, and FIG. 7 shows the evaluation results when x = −0.003 and y = 0.020. 8 shows the evaluation results when x = 0.000 and y = 0.000. 6 to 8, when the thickness of the piezoelectric substrate is larger than 30 μm, both the fixing rate and the c / a front / back difference are low values. However, when the thickness of the piezoelectric substrate is 30 μm or less, the c / a front / back difference increases in FIGS. 6 and 8, and the fixation rate increases in FIG. Thus, the problem of sticking and diffusing is a problem that became apparent for the first time when a piezoelectric substrate having a thickness of 30 μm or less was fired. The present inventors have found that the governing factor of these problems is the composition of the piezoelectric material, and have come up with the manufacturing method disclosed below.

The manufacturing method of the piezoelectric substrate disclosed in this specification is M _{1−y / 2 + x} (N _1−y N _by ) O _{3 + x} (where 0 ≦ y ≦ 0.045, and M is Pb _1−p Sr. _p represents 0 ≦ p ≦ 0.03, N represents Ti _1-q Zr _q , and 0.45 ≦ q ≦ 0.60). And a step of obtaining a piezoelectric substrate having a thickness of 30 μm or less and an area / thickness ratio of 1 × 10 ⁷ μm or more by firing the sheet-shaped material placed on a setter. ing. The variable x is a value in the hatched region R and on the boundary line of the hatched region R shown in the following figure.

The area / thickness ratio is a value obtained by dividing the area (μm ² ) of the piezoelectric substrate when the piezoelectric substrate is viewed in plan by the thickness (μm) of the piezoelectric substrate.

  FIG. 1 shows the result of an experiment conducted by the inventor of the present invention superimposed on the above-described figure. In FIG. 1, Δ (upward triangle) indicates that the piezoelectric substrate is fixed to the setter, and ▽ (downward triangle) indicates that atom diffusion from the piezoelectric substrate to the setter occurs. The ● (black dots) means that none of these occurred (that is, the piezoelectric substrate could be suitably manufactured). As shown in the figure, if the variables x and y are values in the hatched region R and on the boundary of the hatched region R, a piezoelectric substrate having a thickness of 30 μm or less is preferable without causing problems of sticking and diffusion. Can be manufactured. Note that if 0 ≦ p ≦ 0.03 and 0.45 ≦ q ≦ 0.60, the variables x and y are within the hatched region R and the boundary between the hatched regions R, regardless of the variables p and q. It was confirmed that a piezoelectric substrate with a thickness of 30 μm or less can be suitably manufactured if the value is on the line. According to the above invention, a piezoelectric substrate of 30 μm or less can be manufactured.

In the production method described above, the setter is made of stabilized zirconia having a purity of 99.9 mol% or more, the weight concentration of Na in the setter is 50 ppm or less, and the weight concentration of Si in the setter is 5 ppm or more, And it is preferable that it is 50 ppm or less. Stabilized zirconia is a composition obtained by adding ₅ to 10 mol% Y ₂ O ₃ to ZrO ₂ .

The figure which shows the evaluation result of the piezoelectric material board manufactured with the manufacturing method of an Example. The flowchart which shows the manufacturing method which concerns on one Embodiment of this invention. The longitudinal cross-sectional view of the setter 20 and the green sheet 10 arrange | positioned inside the sheath 40. FIG. The top view which shows arrangement | positioning of each member on the setter 20. FIG. The figure which shows the evaluation result of an Example. Pb _1-y / ₂ + _x shows the evaluation results of (N 1-y Nb y) O 3 + x (x = 0.0045, y = 0.020). Pb _1-y / ₂ + _x shows the evaluation results of (N 1-y Nb y) O 3 + x (x = -0.003, y = 0.020). _{Pb 1-y / 2 + x} (N 1-y Nb y) O 3 + x (x = 0.000, y = 0.000) shows the evaluation results of.

FIG. 2 shows a manufacturing method according to an embodiment of the present invention. In this manufacturing method, a piezoelectric substrate having a thickness of 30 μm or less can be manufactured. The ratio S / T between the thickness T (μm) of the piezoelectric substrate to be manufactured and the area S (μm ² ) of the piezoelectric substrate can be 1 × 10 ⁷ (μm) or more. The area S of the piezoelectric substrate is an area of the piezoelectric substrate when the piezoelectric substrate is viewed in plan along the thickness direction of the piezoelectric substrate. In the manufacturing method shown in FIG. 2, such a PZT piezoelectric substrate can be preferably manufactured.

In step S2, a piezoelectric powder (that is, a powder having a composition that becomes a piezoelectric body when sintered) is synthesized. For example, a piezoelectric powder can be synthesized by mixing various material powders and heating the mixed material powders. As a specific embodiment, for example, first, each of material powders composed of PbO, SrCO ₃ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ is finely wet pulverized by a ball mill, a bead mill, etc. Uniform and disperse the particle size of the powder. Next, each material powder is dried, and then each material powder is mixed using a dry crusher such as an atomizer. Next, the mixed material powder is calcined (synthesized) at about 950 ° C. By such a procedure, the piezoelectric powder can be synthesized. Step S2 is performed by adjusting the blending ratio of each material powder so that the synthesized piezoelectric powder has a composition of M _{1−y / 2 + x} (N _1−y Nb _y ) O _{3 + x} . M represents Pb _1-p Sr _p and N represents Ti _1-q Zr _q . The variable p is adjusted to a value in the range of 0 ≦ p ≦ 0.03. The reason for adjusting the variable p within the range of 0 ≦ p ≦ 0.03 is that when the variable p exceeds 0.03, oxygen defects in the piezoelectric body increase, resulting in coarsening of the particle size and deterioration of the characteristics. It is. The variable q is adjusted to a value within the range of 0.45 ≦ q ≦ 0.60. The reason why the variable q is adjusted to a value of 0.45 or more is to prevent the grain size of the piezoelectric body from becoming coarse. The reason why the variable q is adjusted to a value of 0.60 or less is to prevent the decomposition of PbO during firing and to form a piezoelectric body having a perovskite structure. The variable q is preferably 0.51 ≦ q ≦ 0.55. According to such a configuration, since the sintered piezoelectric body has a composition in the vicinity of MPB (morphotopic phase), a piezoelectric substrate having a high piezoelectric constant can be manufactured. More preferably, 0.51 ≦ q ≦ 0.53. According to such a configuration, the fired piezoelectric body becomes tetragonal, and the amount of electric field induced strain of the piezoelectric substrate becomes larger when a high electric field is applied. Since a high electric field can be easily applied to a thin piezoelectric substrate having a thickness of 30 μm or less, it is desirable that the amount of electric field induced strain be large when a high electric field is applied. However, the values of these variables q are suitable when attention is paid to the amount of electric field induced strain when a high electric field is applied. When attention is paid to fixation to the setter during manufacture and diffusion of atoms between the setter and the piezoelectric substrate, the variable q satisfies at least the condition of 0.45 ≦ q ≦ 0.60. Just do it.

Here, the variables x and y will be described. A piezoelectric body having a composition of M _{1-y / 2 + x} (N _1-y Nb _y ) O _{3 + x} (where M represents Pb _1-p Sr _p and N represents Ti _1-q Zr _q ), It has a perovskite structure. This composition, with respect to a composition of a typical _{PZT Pb (Ti 1-q Zr} q) O 3, and Sr, and Nb, in which the addition of PbO. The variable x represents the addition amount of PbO, and the variable y represents the addition amount of Nb. Note that the subscript “-y / 2” is attached to M because Nb is pentavalent, and therefore a defect of −y / 2 is formed at the divalent M site. When the defect is represented by α, M in the composition formula can also be represented as (Pb _1-p Sr _p ) _{1-y / 2 + x} α _{y / 2} . As will be described later, the variables x and y are adjusted so as to have values in the hatched region R and the boundary of the hatched region R shown in FIG.

  In step S4, a green sheet is formed using the piezoelectric powder synthesized in step S2. For example, a green sheet can be formed by the following procedure. That is, a solvent, a dispersion material, a binder, and a plasticizer are added to the synthesized piezoelectric powder, and wet mixing is performed using a ball mill, a bead mill, or the like. Next, the mixed material is applied onto a PET film by a doctor blade method to form a green sheet. At this time, the thickness of the green sheet is set to 38 μm or less. Thus, when the thickness of the green sheet is 38 μm or less, the thickness of the piezoelectric substrate obtained after firing is 30 μm or less.

  In step S6, the green sheet formed in step S4 is cut. For example, the green sheet can be cut into a square having a side of about 40 mm. A known method can be used for cutting the green sheet. In addition, what is necessary is just to cut a green sheet with PET film, when the material mixed on PET film was apply | coated as mentioned above at the time of green sheet shaping | molding. Then, after cutting, the green sheet may be peeled from the PET film.

In step S8, the green sheet is degreased. The degreasing of the green sheet can be performed, for example, by the following procedure. That is, first, a green sheet is placed on a setter made of stabilized zirconia having a purity of 99.9% or more. Next, a porous setter is placed on the green sheet. That is, the green sheet is sandwiched between two setters. In this state, the green sheet is heated to 500 ° C. in an air ventilation atmosphere. Thereby, the green sheet can be degreased. Thus, if the green sheet is degreased with the porous setter placed thereon, it is possible to prevent the warpage of the green sheet during degreasing. Further, since the setter placed on the green sheet is porous, the gas generated from the green sheet at the time of degreasing is released to the outside through the pores inside the porous setter. Therefore, it can degrease suitably. In addition, since a green sheet may break if a porous setter is too heavy, it is preferable to use a porous setter having an appropriate weight. In addition, what is necessary is just to remove the porous setter mounted on the green sheet after degreasing | defatting, when degreasing in the state which mounted the porous setter. The steps S2 to S8 described above correspond to a step of forming a material having a composition of M _{1-y / 2 + x} (N _1-y Nb _y ) O _{3 + x} into a sheet shape.

In step S10, the piezoelectric substrate is baked by heating the degreased green sheet. That is, the piezoelectric powder in the green sheet is sintered to be converted into ceramics, thereby obtaining a plate-like piezoelectric substrate. The firing of the piezoelectric substrate can be performed, for example, by the following procedure. That is, first, as shown in FIG. 3, a plurality of stabilized zirconia setters 20 that have been degreased are stacked in the sheath 40 with the green sheet 10 placed on the inside of the MgO sheath 40. To do. Note that four spacers 30 are arranged on the setter 20 as shown in FIG. 4, and a space is secured between the green sheet 10 and the setter 20 thereabove as shown in FIG. As shown in FIG. 4, on the setter 20, in addition to the green sheet 10, a dummy sheet 22 created by the same process as the green sheet 10 can be arranged around the green sheet 10. The dummy sheet 22 preferably has the same composition as the green sheet 10. Next, the atmosphere powder (powder for adjusting the atmosphere inside the sheath at the time of firing) is placed inside the sheath in a state where it is placed in a MgO dish (not shown). In this state, the sheath is sealed and the inside of the sheath is heated. Thereby, the piezoelectric powder in the green sheet is sintered, and a plate-like piezoelectric substrate is completed. Note that the thickness of the green sheet decreases during firing. Since the thickness of the green sheet before firing is 38 μm or less, the thickness of the piezoelectric substrate after firing is 30 μm or less. Further, the green sheet before firing is a square having a side of about 40 mm, but this size is also reduced during firing. The fired piezoelectric substrate has a square shape with a side of about 32 mm. Therefore, the area / thickness ratio of the fired piezoelectric substrate is about 3 × 10 ⁷ μm (that is, 1 × 10 ⁷ μm or more). The firing temperature is not particularly limited, but can be appropriately set depending on the composition and particle diameter of the piezoelectric powder, the denseness required for the fired piezoelectric substrate, and the like. For example, if a dense piezoelectric substrate having the above composition of 95% or more of the theoretical density is manufactured, it can be fired in the range of 1175 ° C. to 1250 ° C. When the temperature is lower than 1175 ° C., the denseness is inferior, and when fired at 1250 ° C. or higher, the particles may grow abnormally or the decomposition of Pb cannot be suppressed, and a different phase may precipitate.

  If the dummy sheet 22 having the same composition as the green sheet 10 is disposed around the green sheet 10 as described above, the concentration of PbO gas around the green sheet 10 can be increased during firing. Thereby, the PbO is prevented from coming off from the green sheet 10, and the warpage of the green sheet 10 can be suppressed.

  Moreover, when the space | interval H1 between the setters 20 shown in FIG. 3 is too narrow, when the setter 20 warps at the time of baking, the green sheet 10 will contact the upper setter 20 and the green sheet 10 will deform | transform. If the interval H1 is too wide, the space on the green sheet 10 is widened, and the PbO gas concentration around the green sheet 10 becomes unstable, so that the green sheet 10 is warped. Therefore, the distance H1 between the two setters 20 is preferably 30 μm or more and 200 μm or less, more preferably 50 μm or more and 150 μm or less.

  Further, as shown in FIG. 3, the thickness D1 of the uppermost setter 20a and the thickness D2 of the lowermost setter 20b are preferably at least twice as large as the thickness D3 of the other setters 20. If a thick and heavy setter 20a is arranged at the top, the lower setter 20 can be pressed by the load of the setter 20a. Thereby, the warp of each setter 20 at the time of firing can be prevented. Further, by increasing the thickness of the lowermost setter 20b, the load of each upper setter 20 can be received without deformation of the setter 20b. By suppressing the warpage of each setter 20 as described above, the warpage of the green sheet 10 can be suppressed.

Moreover, in said manufacturing method, it is preferable that centerline average roughness Ra which shows the surface roughness of the upper surface of the setter 20 is 0.02 micrometer-5 micrometers, and maximum height Rmax is 10 micrometers or less. For this purpose, it is preferable to form the setter 20 by forming a sheet using ZrO ₂ material powder having a particle size of 0.5 μm to 1.5 μm and firing the sheet. By forming the setter 20 in this way, the surface roughness of the setter 20 can be set to an appropriate value. When the upper surface of the setter 20 is formed by polishing or blasting, it is difficult to reduce the maximum height Rmax, which is not preferable. Moreover, as for the amount of impurities contained in the setter 20, it is preferable that Na is 50 ppm or less and Si is 50 ppm or less. This is because when there is too much Na or Si, mutual diffusion is easily placed between the setter 20 and the green sheet 10. Moreover, it is preferable that Si contained in the setter 20 is 5 ppm or more. This is because if the amount of Si is too small, the density of the setter 20 becomes low, and PbO enters the setter 20 and the PbO gas concentration in the atmosphere easily changes.

According to the manufacturing method described _{above, M 1-y / 2 +} x (N 1-y Nb y) O 3 + x ( where, M represents _{Pb 1-p} Sr p, N represents _{Ti 1-q} Zr q.) A piezoelectric substrate having the following composition can be preferably manufactured. That is, according to this manufacturing method, it is possible to prevent atoms from diffusing from the piezoelectric substrate (that is, the green sheet) to the setter during firing while preventing the piezoelectric substrate and the setter from sticking. Thereby, the uniformity of the composition in the piezoelectric substrate can be ensured. In addition, since diffusion of atoms can be prevented in this way, a piezoelectric substrate having no difference in particle diameter between the front side surface and the back side surface can be manufactured. The surface of the piezoelectric substrate means the surface that was not in contact with the setter at the time of firing (ie, the upper surface), and the back surface of the piezoelectric substrate was the surface that was in contact with the setter at the time of firing (ie, the lower surface). means. More specifically, according to this production method, the difference in the average particle size between the front side surface and the back side surface is within 10% of the average value of the front side surface, and between the front side surface and the back side surface. Piezoelectric substrates in which the difference in the standard deviation of the particle diameter is within 10% of the standard deviation on the front side surface can be manufactured. The piezoelectric substrate manufactured using this method can then be used as a piezoelectric element by forming electrodes on both sides and cutting it into a predetermined shape. Furthermore, the piezoelectric element can be used as a piezoelectric actuator, a sensor, an ultrasonic motor, or the like by bonding to a circuit board so that a voltage can be applied between electrodes formed on both sides. In particular, since a high electric field can be applied to such a thin piezoelectric substrate, a piezoelectric element manufactured from this piezoelectric substrate is preferably used in fields where downsizing and a large amount of displacement are required. be able to. Further, according to this manufacturing method, a large piezoelectric substrate can be manufactured, so that a large number of piezoelectric elements can be obtained, and the piezoelectric elements can be manufactured at low cost.

  Also, according to the above method, a piezoelectric substrate having a thickness of 30 μm or less can be manufactured by firing. That is, a thin piezoelectric substrate can be obtained without performing surface polishing or the like (that is, thinning) of the piezoelectric substrate after firing. Therefore, this manufacturing method can manufacture a thin piezoelectric substrate with excellent production efficiency. Moreover, in the piezoelectric substrate manufactured in this way, both the front side surface and the back side surface are fired surfaces (surfaces exposed to the surface of the piezoelectric substrate during firing). On the fired surface, there are minute irregularities due to the particle diameter of the piezoelectric body constituting the piezoelectric substrate. For this reason, when the electrode is formed on the surface of the piezoelectric substrate, the adhesion of the electrode to the piezoelectric substrate is high.

  Embodiments embodying the present invention will be described below. The following examples are specific examples for explaining the present invention, and do not limit the present invention.

  Various values were adopted as variables x and y to synthesize piezoelectric powder, and the synthesized piezoelectric powder was fired at 1200 ° C. for 3 hours to manufacture a piezoelectric substrate. The manufacturing method mentioned above was used for the manufacturing method. The manufactured piezoelectric substrate had a square shape of about 40 mm and a thickness of about 15 μm. In all manufactured piezoelectric substrates, q = 0.525 and p = 0.02. When q = 0.525, the crystal lattice of the piezoelectric body is a tetragonal crystal.

  Each of the manufactured piezoelectric substrates was evaluated for adhesion and c / a front / back difference. FIG. 5 shows the result of evaluating the adhesion and c / a front / back difference for each piezoelectric substrate. The sticking in FIG. 5 means that the piezoelectric substrate sticks to the setter during firing in step S10. The presence or absence of sticking was determined by checking whether or not the piezoelectric substrate was moved after firing in step S10. O of the evaluation result of sticking represents that no sticking occurred in all of the ten test sheets, and X represents that sticking occurred even in one sheet.

  Further, the c / a front / back difference means a difference in c / a between the front side surface and the back side surface of the piezoelectric substrate. c / a is an axial ratio of a tetragonal crystal that is a crystal lattice of the piezoelectric body (a value obtained by dividing a length c of an axis that forms a square by a length c of an axis that does not form a square). In the evaluation of FIG. 5, it was determined whether or not the c / a front / back difference was greater than 0.001 (that is, whether or not there was a difference in c / a between the front and back sides of the piezoelectric substrate). O in the evaluation result of c / a front / back difference means that the c / a front / back difference is 0.001 or less, and X means that the c / a front / back difference is larger than 0.001. In addition, since the measurement error of c / a is about 0.001, a c / a front-back difference of 0.001 or less means that there is no measurable difference. When Ti diffuses from the piezoelectric substrate to the setter during firing, c / a on the back side of the piezoelectric substrate changes. Therefore, in this case, the c / a front / back difference increases. If the c / a front / back difference is large, the piezoelectric constants are different between the front side surface and the back side surface, which is not preferable because the piezoelectric body is deformed to be warped when a voltage is applied. In addition, c / a was calculated from the ratio of the detected intensity of the (200) plane and the detected intensity of the (002) plane in X-ray diffraction. The X-ray diffractometer uses X-part MPD Pro manufactured by Spectris, and the X-ray source measures CuKα, acceleration voltage 45 kV, and the range of 40 ° -50 ° by the θ / 2θ method, so that the accuracy is high. The measurement time was set so that the main peak was 100,000 counts or more.

  FIG. 1 is a graph showing the evaluation results of FIG. In FIG. 1, Δ (upward triangle) indicates that sticking has occurred, ▽ (downward triangle) indicates that the c / a front / back difference is large, and ● (black dot) does not cause these problems. (That is, the piezoelectric substrate was successfully manufactured). As shown in the figure, the smaller the variable x, the more likely the sticking occurs, and the larger the variable x, the more likely the c / a front / back difference tends to increase. However, these problems can be solved by setting the variable x to an appropriate value. It turns out that it does not occur. The appropriate range of the variable x varies depending on the value of the variable y. That is, by adjusting the variable y to a value of 0 ≦ y ≦ 0.045 and adjusting the variable x to a value within the range indicated by the hatched region R in FIG. It has been found that the piezoelectric substrate can be suitably manufactured without causing the above.

  FIG. 1 shows the results when p = 0.02 and q = 0.525. However, the variable p is in the range of 0 ≦ p ≦ 0.03, and the variable q is 0. A piezoelectric body having a thickness of preferably 30 μm or less as long as the variables x and y are within the hatched region R, regardless of the values of the variables p and q, as long as they are within the range of 45 ≦ q ≦ 0.60. It has been found that it is possible to produce a substrate (i.e. no sticking problems occur and no change in the crystal lattice axial ratio).

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

Claims (2)

A method for manufacturing a piezoelectric substrate, comprising:
_{M 1-y / 2 + x} (N 1-y Nb y) O 3 + x ( where a 0 ≦ y ≦ 0.045, M represents Pb _{1 over} p Sr _p, is 0 ≦ p ≦ 0.03, N represents Ti _1-q Zr _q , and 0.45 ≦ q ≦ 0.60).
A step of obtaining a piezoelectric substrate having a thickness of 30 μm or less and an area / thickness ratio of 1 × 10 ⁷ μm or more is obtained by firing the sheet-shaped material placed on a setter. And
Variable x, Ri value der borderline of the hatched region R in and shaded area R shown in the following (Formula 1),
The setter is composed of stabilized zirconia,
A method characterized by that.

The setter is composed of stabilized zirconia having a purity of 99.9 mol% or more,
2. The method according to claim 1, wherein a weight concentration of Na in the setter is 50 ppm or less, and a weight concentration of Si in the setter is 5 ppm or more and 50 ppm or less.

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